TWCB Source and Destination NAT

Standard TWCB operation requires that a cache server have a route back to the client through the TWCB router. A second consideration is that client addresses are often unknown to the cache server. The TWCB source and destination NAT feature addresses these two issues. The configuration of TWCB source and destination NAT allows the client, TWCB router, and cache server to reside anywhere in the network and still provide for the forwarding of an HTTP request from the client to the web cache server. TWCB source and destination NAT also provides for the reverse forwarding from the web cache server to the client, assuring that the packet flow will pass through the TWCB router.

TWCB Configuration Overview and Predictor Round-Robin Overview illustrate examples of standard TWCB configurations. In both cases, clients and cache servers are directly connected to the TWCB router, assuring that the cache server both knows the address of the requesting client and has a route back to that client through the TWCB router.

TWCB Source and Destination NAT Overview illustrates a typical TWCB source and destination NAT configuration. Any requests directed to Cache1, can not assure that the reverse path will transit the TWCB router. Only Cache2, being directly connected to the TWCB router, can assure that the reverse path will transit the TWCB router. Therefore, this TWCB configuration requires source and destination NAT to account for any requests going to Cach1. The administrator configures TWCB Router3 for source and destination NAT by specifying both a Destination NAT address range and a Source NAT address range.

1. Client1, directly attached to Router2, makes an HTTP request to the TWCB Router3 for www.extremenetworks.com. The packet flow source address is the Client1 IP address. The packet flow destination address is the TWCB destination NAT address configured on TWCB Router 3. When the packet reaches Router3, the TWCB router can direct the request to either web cache in the configuration. TWCB selects Cache1 for this request.
2. Before it forwards the request to Cache1, TWCB selects a source NAT address for the HTTP request packet flow from the configured range and sets the destination address to a cache server on Cache1 and forwards the request to the cache server.
3. The Cache1 cache server retrieves the request and reverse forwards it back to the TWCB router using its own address as the source and the source NAT address as the destination.
4. When the packet flow arrives at the TWCB router, it forwards it on to Client1 using the destination NAT address as the packet flow source and Client1‘s address as the destination.
   

   TWCB Source and Destination NAT Overview